1. Field of the Invention
The present invention relates to add-on window structures to an aircraft, and in particular, to a heated aircraft bilayer window appendage to be mounted outboard of an aircraft windshield.
2a. Technical Considerations
It is common practice in the aircraft industry to heat part or all of an aircraft window in order to prevent fogging or ice from forming on the window that will impede clear viewing therethrough. This is particularly important in the aircraft windshield. In aircraft where the heating is not incorporated into the main windshields, add-on windows or appendages must be used to heat the viewing portion of the windshield. These add-on windows may be fabricated from bonded acrylic plies with the heating arrangement, such as heating wires, bonded therebetween. With such an arrangement, the exposed acrylic surface is subjected to scratching and environmental degradation that will shorten the useful operating life of a window appendage.
It would be beneficial to provide an arrangement to heat aircraft windows that do not otherwise have heating capabilities while also providing good durability and long service life.
2b. Patents of Interest
U.S. Pat. Nos. 3,721,595 to Tarnopol and 4,057,671 to Shoop teach heating a glass panel. In Tarnopol et al. the glass panel is the rear window of an automobile and the window is heated by a circuit pattern of an electroconductive frit composition deposited on the inboard surface of the rear window. In Shoop, a laminated window assembly is heated by plurality of electroconductive wires extending across the window and connected to a bus bar.
U.S. Pat. Nos. 4,078,107 and 4,128,448 to Bitterace et al. teach a transparent window with a static electricity dissipating circuit and a heating circuit. The circuits are embedded in opposing major surfaces of an acrylic plastic sheet which is thereafter laminated between two glass plies.
U.S. Pat. No. 3,971,178 teaches an add-on window to convert a single glazed window into a multiple glazed window. An additional pane, with a spacer attached, is hermetically sealed to an installed pane so as to provide a moisture resistant barrier and/or improved structural strength.